Coexisting crystalline solution phases activated by divalent europium

ABSTRACT

A blue-emitting Eu2 activated, fluorescent phosphor of coexisting crystalline phases of the spinel structure of MgA12O4 and the corundum structure of Alpha A12O3 is useful in fluorescent and mercury vapor lamps. The essential cations of each structure are A1, Mg and Si. In the corundum phase, the Si4 and Mg2 ions displace A13 ions, are disposed in the corundum lattice of A12O3 and are present in significant quantities, but less than the limit of mutual solubility of the Si4 and Mg2 ions in the corundum lattice. In the spinel phase, Si atoms and site vacancies displace Mg atoms in the spinel lattice and are present in significant quantities, but less than the limit of solubility of Si atoms and vacancies in the spinel lattice.

United States Patent [72] Inventor [21 Appl. No. [22] Filed [45 1Patented [73] Assignee [54] COEXISTING CRYSTALLINE SOLUTION PHASESACTIVATED BY DIVALENT EUROPIUM 3 Claims, 3 Drawing Figs.

[52] US. Cl 313/109, 252/301.4F [51] Int. Cl H0lj 1/62 [50] Field ofSearch 252/301.4 (IV), 301.4; 313/108, 109

[56] References Cited UNITED STATES PATENTS 2,961,412 11/1960 Hummel252/301.4(IV) 3,359,211 12/1967 Jaffe ..252/301.4(IV) 3,503,894 3/1970Wachtel ..252/30l.4(1V) Primary Examiner-Robert D. EdmondsAttorneys-Norman .l. OMalley and Owen J. Meegan ABSTRACT: Ablue-emitting Eu activated, fluorescent phosphor of coexistingcrystalline phases of the spinel structure of MgAl O and the corundumstructure of a A1 0 is useful in fluorescent and mercury vapor lamps.The essential cations of each structure are Al Mg and Si. In thecorundum phase, the Si and Mg ions displace Al ions, are disposed in thecorundum lattice of A1 0, and are present in significant quantities, butless than the limit of mutual solubility of the Si and Mg ions in thecorundum lattice. in the spinel phase, Si atoms and site vacanciesdisplace Mg atoms in the spinel lattice and are present in significantquantities, but less than the limit of solubility of Si atoms andvacancies in the spinel lattice.

PATENTEU M 4m Mlxed CORUN SPIN -CORUNDUM SPINE L 560 WAVELENGTH mNANOMETERS INVENTOR THOMAS L. BARRY BYaL/%- ATTORNEY COEXISTINGCRYSTALLINE SOLUTION PI-IASES ACTIVATED BY DIVALENT EUROPIUM CROSSREFERENCE TO RELATED APPLICATIONS This application is a continuation inpart of my copending application Ser. No. 506,868, filed Nov. 8, 1965,now abandoned.

BACKGROUND OF THE INVENTION This invention relates to fluorescentphosphors and especially those excited by low and high pressure mercurydischarges. Specifically, this invention relates to divalent europiumactivation of two coexisting crystalline solution phases. One phasepossesses the corundum structure (aA1 and the other the normal spinelstructure A "B O,). The resultant mixture yields a phosphor ofcomparable blue color to the commercially available blue phosphors. Suchmaterials can find their primary usefulness in blends with phosphorswhich emit other colors to produce a desired overall emission.

DESCRIPTION OF THE PRIOR ART Earlier work on divalent europiumactivation of aluminosilicate phosphor compositions has been disclosedby Jaffe, US. Pat. No. 3,359,211. The compositions covered arerepresented by the formulation x A1 0 (lx)SiO :y c Eu. Different phasescan be obtained depending upon the firing temperature and the raw-mixcomposition. However, a spine]- like phase is not disclosed and adifferent polymorph of alumina (O-AI O is obtained. A green-yellowemitting europium aluminosilicate phosphor (EuA1 Si O has also beendisclosed by Jaffein US. Pat. No. 3,359,210.

SUMMARY OF THE INVENTION The high level of luminescence of the materialof the coexisting crystalline solution phases, compared to beunsubstituted structures when observed independently, that is when acrystalline solution is not employed, is due to the defect chemistryinvolved in the incorporation of the foreign ions. In the corundum phase(or-A1 0 the crystalline solution is formed by balancedsionic chargesubstitution (2 Al =si Mg) while in the normal spinel structure (A? B"O4), the crystalline solution may be formed byseveral'substitutionschemes. The actual substitution scheme appears to be a combination ofthese. Two possibilities are (1 balanced ionic charge substitution, asin the corundum structure mentioned above, if the structure divalent thespinel crystalline solution phase is derived from the -yAl O defectspinel structure or more likely (2) cation vacancy formation 2Mg =Si +|jif the structure is derived from MgAl,O spinel with tetravalent siliconion substituting for devalent magnesium, as above, in the tetrahedralsites. The formulation of these phases is given below: Corundum phase:(Al f ,,,Si AQwMg O zEu fi.

where the sum of the-cations is 2, and w is within the range ofdetectable quantities and the mutual solubility limit of Si and Mg incorundum. v is between about 0.001 and 0.20. spinel P as gmm z .r) W 2V1 4 u where 1:] represents the vacancies formed in the cation latticeto preserve electroneutrality, and y is between about 0.001 and 0.20,and x is within the range from detectable quantities to the solubilitylimit of Si in MgAl O.,.

In the formulas used, the roman numerals indicate the coordinationnumbers, that is the number of anions which surround the given cation orcations when these are located in the given sites.

While these formulas represent the approximate compositions ofthe'respective phases in a given fluorescent compositions, which can beidentified by x-ray diffraction, the actual cation distribution may varysubstantially from the formulas as written without lying outside thescope of the invention.

Quite surprisingly, the unsubstituted corundum and spinel phases do notexhibit substantial luminescence individually. The accompanying FIG. 3compares the unsubstituted phases with the coexisting cyrstallinesolution phases. The relative responses to 254 Nm. excitation of thecorundum is about 0.5 units and the spinel is about 0.3 units. Themixture comprised of these structures, however, when crystallinesolution is employed, produces a relative response of about 3.8 units.

Referring now to FIG. 1, a typical fluorescent lamp containing mercuryvapor is shown including a glass envelope 6 having end caps 7 and 8 withelectrical lead-in wires 9 and connected to cathodes (not shown). Alayer 10 of the phosphor of the present invention is coated upon theinternal surface of the glass envelope 6. In FIG. 2, the high pressuremercury lamp is shown which includes the conventional arrangement of anarc tube (not shown) supported upon the metal harness 4. Surrounding thearc tube and harness is a bulbous envelope 12, with a coating 5 of thephosphor of this invention disposed upon the internal surfaces thereof.

To prepare the material, alumina, basic magnesium carbonate, and silicicacid can be mixed together and fired with a source of europium, usuallyeuropium nitrate, to produce a novel blue emitting phosphor. Thenecessary amount of each of the above-identified starting materials canbe weighed and mixed with glass beads for blending. When blended, thematerial is separated from the beads and placed in an alumina boat forfiring. The blend is preheated in a furnace for approximately one hourat about 650 C. to decomposevthe basic alkaline earth carbonate andremove other volatiles from the starting mixture. The decomposed sampleis then fired in a tube furnace for approximately 1 hour between 1 C.and 1300 C. in a reducing atmosphere of hydrogen and nitrogen. The fusedsilica tube can then be removed from the furnace and cooled to roomtemperature in the reducing atmosphere.

The following test results were obtained and compared to a standard blueemitting phosphor (Sr P O,:Sn):

TABLE I Plaque Sample Formulation Red Green Blue A Sr2PzO1:Sn +n.05 13100 230 17 105 C 32 220- D 18 275 E 5Al;O -3.43MgO-1.5S1O :Eu h 16 160315 15 145 305 F 5A1zOr3.43MgO-2.0SiOz: E11 o.ot

When equal atom fractions of magnesium and silicon areemployed in theformulation, the following results were obtained:

TABLE II Plaque Sample Formulation Red Green Blue A---.... A12Oa:E11 o.o6 22 47 B 0.99A1z03-0.01S1Oz-(L01Mg0:Eu 'om.. 8 51 64 C...0.95A1z03-0.50Si0z-0.05Mg0ZEl1 o o 15 100 140 D- 0.90111 0-0.10SiO;-0.10MgO Eu o 21 160 260 0.8011120 -0.20S10z-020Mg0 Eu 15 160290 EXAMPLE 1 Mix together in a blender the following ingredients:

2.548 gms.-3MgCO -Mg(OI-I) -3H O 1.676 grns.SiO 11.383 gins-A1 0 Theseingredients are blended together for minutes and then fired for l hourat 650 C. in air. They are then broken up and refired in a reducingatmosphere of percent hydrogen and 80 percent nitrogen.

EXAMPLE II The same procedure as outlined in Example I is followedexcept the ingredients are:

6.138 gms.3MgCO -Mg(OH -3H O 1.767 gms-SiO 9.972 gms.Al O

gm.Eu(NO -6H O spinel structure of MgAl O and the corundum structure of(Jr-A1 the essential cations of each structure being Al, Mg and Si, thephosphor being activated by europium, said corundum phase having theformula g W12 s omF-mw wherein the Si" and Mg ions displace Al ions andare disposed in the corundum lattice of A1 0 but in quantities less thanthe limit of mutual solubility of said ions in said corundum lattice,the Eu ions displacing Mg ions in the corundum lattice within thespecified range, said spinel phase having the formula gX X l W A12 v] 40.o01"o.zo

where represents the vacancies formed in the cation lattice to preserveelectroneutrality and wherein the Si atoms and the Edisplace Mg atoms inthe spinel lattice of MgAl O but in quantities less than the limit ofsolubility of said atoms and E1 in said spinel lattice, the Eu ionsdisplacing Mg atoms in the spinel lattice within the specified range,each of said phases being present in the phosphor in amounts sufficientto produce a level of luminescence above that produced by each phaseseparately.

2. A fluorescent lamp including a glass envelope, electrodes disposed ateach end of said means, to produce an electric discharge in saidenvelope and a luminescent layer coatedupon said envelope, said layerincluding a phosphor consisting essentially, and having significantquantities, of both of the coexisting solution phases of the spinelstructure of MgAl O and the corundum structure of a-Al O the essentialcations of each structure being Al, Mg and Si, the phosphor beingactivated by europium, said corundum phase having the formula g )12 VI s0.001 0.20 wherein the Si and Mg ions displace Al ions and are disposedin the corundum lattice of A1 0 but in quantities less than the limit ofmutual solubility of said ions in said corundum lattice, the Eu ionsdisplacing Mg ions in the corundum lattice within the specified range,said spinel phase having the formula gX XUl [v A12VI 4 o.001-"0.20

where 1:! represents the vacancies formed in the cation lattice topreserve electroneutrality and wherein the Si atoms and the El displaceMg atoms in the spinel lattice of MgAl O but in quantities less than thelimit of solubility of said atoms and U in said spinel lattice, the Euions displacing Mg. atoms in the spinel lattice within the specifiedrange, each of said phases being present in the phosphor in amountssufficient to produce a level of luminescence above that produced byeach phase separately.

3. A mercury lamp including an arc tube surrounded by a bulbous glassjacket, said jacket having a luminescent layer coated upon saidenvelope, said layer including a phosphor consisting essentially, andhaving significant quantities, of both of the coexisting solution basesof the spinel structure of MgAl O and the corundum s ructure 0r-AI O theessential cations of each structure being Al, Mg and Si, the phosphorbeing activated by europium said corundum phase having the formula g )]2a 0.o0i' 0.20 wherein the Si and Mg ions displace Al ions and aredisposed in the corundum lattice of A1 0 but in quantities less than thelimit of mutual solubility of said ions in said corundum lattice, the Euions displacing Mg ions in the corundum lattice within the specifiedrange, said spinel phase having the formula where 0.20 where representsthe vacancies formed in the cation lattice to preserve electroneutralityand wherein the Si atoms and the [I] displace Mg atoms in the spinellattice of MgAl O but in quantities less than the limit of solubility ofsaid atoms and [I in said spine] lattice, the Eu ions displacing Mgatoms in the spinel lattice within the specified range, each of saidphases being present in the phosphor in amounts sufficient to produce alevel of luminescence above that produced by each phase separately.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 577,169 Dated MAY 4:, 1971 Inventor(s) THOMAS L. BARRY It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

At column 1, line 16 insert a parenthesis sign before "A B O line 43:change "si to "Si line 50: change "divalent" to "of"; line 57: changeline 62: change "Mgl gx y" t0 "Mg -gx-y".

At column 2, line 5: change "Nm" to "run" At column 5, line 23 change"A1 to "A1 0 7 line 54: between "where" and "represents" insert -I;3line 56 change "L to "El line 44: between "said" and "means" delete theparenthesis sign and insert -envelope--.

At column 4, line 339: delete "0.20 where and insert 3 Signed and sealedthis 9th day of November 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,J'R. ROBERT GOTTSCHALK Attestinp: Officer Co IL, ss

FORM PO-105O (10-59) -gc 00375-p5 a u s covtmmzm' PRINTING OFFICE: '90!0-35i-J34

1. A phosphor consisting essentially, and having significant quantities,of both of the coexisting solution phases of the spinel structure ofMgAl2O4 and the corundum structure of Alpha -Al2O3, the essentialcations of each structure being Al, Mg and Si, the phosphor beingactivated by europium, said corundum phase having the formula ((Al3)(Si4 )(Mg2 ))2 O3:Eu2 0.001-0.20 wherein the Si4 and Mg2 ions displaceAl3 ions and are disposed in the corundum lattice of Al2O3 but inquantities less than the limit of mutual solubility of said ions in saidcorundum lattice, the Eu2 ions displacing Mg2 ions in the corundumlattice within the specified range, said spinel phase having the formula((Mg)(Si)( ) ) A12 O4:Eu2 0.001-0.20 where represents the vacanciesformed in the cation lattice to preserve electroneutrality and whereinthe Si atoms and the displace Mg atoms in the spinel lattice of MgAl2O4,but in quantities less than the limit of solubility of said atoms and insaid spinel lattice, the Eu2 ions displacing Mg atoms in the spinellattice within the specified range, each of said phases being present inthe phosphor in amounts sufficient to produce a level of luminescenceabove that produced by each phase separately.
 2. A fluorescent lampincluding a glass envelope, electrodes disposed at each end of said )means, to produce an electric discharge in said envelope and aluminescent layer coated upon said envelope, said layer including aphosphor consisting essentially, and having significant quantities, ofboth of the coexisting solution phases of the spinel structure ofMgAl2O4 and the corundum structure of Alpha -Al2O3, the essentialcations of each structure being A1, Mg and Si, the phosphor beingactivated by europium, said corundum phase having the formula ((Al3)(Si4 )(Mg2 ))2 O3:Eu2 0.001-0.20 wherein the Si4 and Mg2 ions displaceAl3 ions and are disposed in the corundum lattice of Al2O3 but inquantities less than the limit of mutual solubility of said ions in saidcorundum lattice, the Eu2 ions displacing Mg2 ions in the corundumlattice within the specified range, said spinel phase having the formula((Mg)(Si)( ) Al2 O4:Eu2 0.001-0.20 WHERE represents the vacancies formedin the cation lattice to preserve electroneutrality and wherein the Siatoms and the displace Mg atoms in the spinel lattice of MgAl2O4, but inquantities less than the limit of solubility of said atoms and in saidspinel lattice, the Eu2 ions displacing Mg. atoms in the spinel latticewithin the specified range, each of said phases being present in thephosphor in amounts sufficient to produce a level of luminescence abovethat produced by each phase separately.
 3. A mercury lamp including anarc tube surrounded by a bulbous glass jacket, said jacket having aluminescent layer coated upon said envelope, said layer including aphosphor consisting essentially, and having significant quantities, ofboth of the coexisting solution phases of the spinel structure ofMgAl2O4 and the corundum structure Alpha -Al2O3, the essential cationsof each structure being Al, Mg and Si, the phosphor being activated byeuropium said corundum phase having the formula ((Al3 )(Si4 )(Mg2 ))2O3:Eu2 0.001-0.20 wherein the Si4 and Mg2 ions displace Al3 ions and aredisposed in the corundum lattice of Al2O3 but in quantities less thanthe limit of mutual solubility of said ions in said corundum lattice,the Eu2 ions displacing Mg2 ions in the corundum lattice within thespecified range, said spinel phase having the formula ((Mg)(Si)( )) Al2O4:Eu2 0.001-where 0.20 where represents the vacancies formed in thecation lattice to preserve electroneutrality and wherein the Si atomsand the displace Mg atoms in the spinel lattice of MgAl2O4, but inquantities less than the limit of solubility of said atoms and in saidspinel lattice, the Eu2 ions displacing Mg atoms in the spinel latticewithin the specified range, each of said phases being present in thephosphor in amounts sufficient to produce a level of luminescence abovethat produced by each phase separately.